Chris Hayes, the Washington editor for The Nation, is a frequent contributor to MSNBC shows, and often fills in for Rachel Maddow on her show. The Upshot reports that he gave $250 to Alabama Democratic candidate Josh Segall this year before he signed his contract with MSNBC.

NBC News producer Mary Murray, who also does reporting for NBC News and MSNBC, gave $250 to John Waltz (D-KY) this year. In 2008 she gave the same amount to Barack Obama's presidential campaign.

Update:New York Times reporter Brian Stelter Tweeted that Hayes, in fact, would not be subbing for Olberman after all.

Later Update: Alex Pareene at Salon notes that CNBC anchor Larry Kudlow donated to former Congressman Christopher Shays (R-CT) in 2009 -- one of a number of donations Kudlow made to Republican candidates over the years.

Even later update: Chris Hayes Tweeted that it was his decision to decline to host "Countdown" tonight, and that his donations were all made prior to his MSNBC contract.